Graded plane, high voltage dc power supply

ABSTRACT

A high voltage electron accelerator system employing a graded plane power supply, a graded plane accelerator, and a single, graded-conductor cable interconnecting the power supply and the accelerator.

United States Patent [50]Field0fSearch........................................... 307/110, 147,149, 150; 313/63; 321/15; 328/233, 256

[72] inventors Joseph T. Peoples;

Charles C. Landry, Austin, Tex.

3 S mm T mm N m m m m mm t P CS "u E mm m T A T 6 e ITD. S m f P e eREJT W41 N55 Uww 12 ll 48 7O %m w 22 0 r 0 C m. l w 87 69.0 8 Qlc 0. deN ee mm. d

AFPA

Primary Examiner-Raymond F. Hossfeld Attorneys-Lowell C. Bergstedt,Walter C. Ramm and 54 GRADED PLANE, HIGH VOLTAGE DC POWER Helmuth wegneSUPPLY 7 Clams 6 Drawmg ABSTRACT: A high voltage electron acceleratorsystem employing a graded plane power supply, a graded plane accelera-321/15, 328/233, 328/256 tor, and a single, graded-conductor cableinterconnecting the [51] Int. H02j 5/00 power supply andthe accelerator.

PATENTEU HAY25 l9?! SHEET 2 [IF 4 MI Pea-Ira ozse k (a a? M61163 ,4arraewr GRADED PLANE, IIIGII VOLTAGE DC POWER SUPPLY Developingindustrial applications for high energy electron beams have produced anexpanding demand for high voltage accelerator systems which are not onlycapable of producing high energy electron beams, but are capable ofcontinuous operation for long periods of time. These accelerator systemsmust also be relatively inexpensive from initial capital investment andoperating and maintenance cost standpoints. The production of highenergy beams of charged particles other than electrons, such as protons,deuterons, and even heavier charged particles, is also of considerableinterest to the scientific community.

One type of high voltage accelerator system which has been developed iscomprised essentially of a high voltage DC power supply, an acceleratorutilizing the DC voltage produced by the power supply to accelerate anion beam, and a cable system for carrying the high voltage power to theaccelerator. Typically, the accelerator also requires additional, lowvoltage power for production of the charged particles to be accelerated,so this must be produced in the power supply and transmitted to theaccelerator via the cable system.

The magnitudes of DC voltage which are of interest for some industrialand other type applications of accelerator systems lie in the l --l,000kv. (kilovolt) range. The problems involved in the production of DCvoltages of these magnitudes by conversion of an available signal froman AC power source are well known to those familiar with this art.Transformers for conversion from low voltage AC to high voltage AC arequite readily available, and circuitry of various types for AC to DCvoltage conversion are well known; but the concurrent problems ofproviding adequate heat dissipation, controlling and stabilizing thehigh DC voltage produced, and keeping the dimensions of the power supplyenclosure down to manageable proportions are not easily reconciled.

Therefore, the principal object of this invention is to provide animproved high voltage DC power supply.

Another object of this invention is to provide an improved high voltageDC power supply for a high voltage accelerator system.

In accordance with this invention a power supply enclosure means forcontaining a quantity of electrically insulating fluid is provided witha plurality of voltage grading means for stabilizing the high voltageproduced within the enclosure, each of the voltage grading meansincluding a plurality of equipotential planes mounted in spaced-apartrelation to each other with a stepwise gradient of voltages from thehigh voltage to a ground reference voltage thereon.

In a preferred embodiment of the invention involving a voltage doublertype of power supply, three series of equipotential planes, associatedcircuitwise with rectifiers, capacitors, and resistors, are mounted intwo separated stacks between opposing walls of the power supplyenclosure which are at ground potential, with the series of planesassociated with the capacitors apportioned between the two stacks. Oneof the two portions of capacitor planes is electrically insulated fromthe nearest walland the other portion utilizes that wall as a groundreference plane. The ground reference planes of the rectifier andresistor series of planes are provided with ground reference voltage bythe opposite wall of the enclosure. The electrical components such asresistors, capacitors, and rectifiers are mounted between individualones of their respective planes.

The primary advantages of the graded plane power supply of thisinvention are the reduction in power supply enclosure dimensions and theincrease in power supply stability or freedom from discharges betweenphysical points within the enclosure which are at different electricalpotentials. This is particularly effectively accomplished in thepreferred embodiment of the graded plane power supply because only twoseparated stacks of planes are required, and the planes which have thehighest DC voltage thereon do not look at ground planes with their flatsides but are provided with intervening planes having lower potentialsthereon. Some of these same advantages would also attach to use of thegraded plane concept wherein the three series of planes are mounted inthree separate stacks, but a rather large separation distance betweenplanes carrying the highest DC voltage and the ground reference planesseen by their flat sides would have to be provided. Thus, it can be saidthat some grading of the power supply potentials always works a sizereduction, but overall grading of the potentials provides the greatestsize reduction advantage and, at the same time, the important advantageof increased operating stability.

Other objects, features, and advantages of this invention will beapparent from a consideration of the detailed description below togetherwith the accompanying drawings in which:

FIG. 1 is essentially a schematic diagram of a graded high voltageelectron accelerator system including a graded cable DC transmissionsystem;

FIG. 2 is an elevational view of the basic mechanical arrangement of thepower supply shown schematically in FIG. 1;

FIG. 3 is a top view of the power supply of FIG. 2;

FIG. 4 is an elevational view of an accelerator head according to aprior art construction;

FIG. 5 is an elevational view of the basic mechanical arrangement of theaccelerator shown schematically in FIG. 1; and

FIG. 6 is a partly sectioned, elevational view of a graded high voltagecable of a particular type of construction.

Referring now to FIG. 1, the three basic components of a.

graded high voltage accelerator system are shown as a graded highvoltage DC power supply 100, a graded high voltage accelerator 200, anda graded high voltage DC power transmis:

sion cable 300. Power supply 100 is one of a voltage doubler type inwhich an AC line voltage is first transformed to provide a high voltageAC signal, and then the high voltage AC signal is rectified to produce acorresponding DC voltage. The particulars of the operation of a voltagedoubler type of DC power supply need not be given here because they arewell known to those skilled in the art.

As shown in FIG. I, a series of equipotential planes 1-11 areinterconnected by a series of rectifiers 30, a series of resistors 31,and a series of capacitors 32. The primary electrical function providedby this group of elements is the rectification accomplished by therectifiers 30, with the capacitors 32 serving as transient equalizersand with the resistors 31 aiding in the equipotential voltage grading ofthe rectifier planes. Equipotential plane 1 1 also serves as one of theplanes in a series composed of planes 11-20 which are interconnected bythree series of capacitors 40 and a series of resistors 41. It should beunderstood that the rectifier symbol 30 may designate a plurality ofrectifiers in series between respective equipotential planes if suchplurality is needed in terms of the actual voltage parameters andsimilarly for resistors 31 and capacitors 32. Moreover, the number andtypes of such elements may vary from one application to another, asdesired.

Planes 15 and 16 in the capacitor series of planes are directlyconnected by a lead 88 since these planes are functioning at the samepotential. The reason for this will become apparent from a considerationof the physical arrangement later discussed. Plane 20 is actually thebottom of a tank which is at ground reference potential, and plane 1 isassociated with top 28 of the tank which is at ground referencepotential also.

Plane 11, the common plane of the rectifier and capacitor series ofplanes is connected via a resistive element 50 to plane 21 in a seriesof planes 21-27 which are interconnected by resistors 60 and 61. Theresistor symbols 60 and 61 may actually correspond to a plurality ofindividual resistors connected in series between each plane. Plane 27 isassociated with top 28 of the tank and is accordingly at groundreference potential. Plane 6 in the rectifier series and plane 15 in thecapacitor series are connected via cables 72 and 71, respectively, tosecondary winding terminals 73 and 74 on a high voltage transfonner 70.Power for transformer 70 is supplied via cables 81 and 82 from a powersupply external to the tank. A high voltage AC signal across terminals73, 74 is rectified to produce a corresponding high voltage DC signal onequipotential'plane 11 and also on equipotential plane 21. Voltagegrading of equipotential planes 1-11 is a varying voltage grading, whilethat on planes 11-20 and planes 21- -27 is substantially constantvoltage grading with only slight amounts of ripple thereon. Transformer75 is an isolation transformer powered by power supply 85 over cables 86and 87, and it produces an AC signal across its secondary windingterminals 78 and 79.

The electrical aspects of a high voltage electron accelerator 200 arealso shown in FIG. 1. Planes 110-116 are graded equipotential planeswith planes 11-114 serving as accelerating electrodes, plane 115together with cup 122 sewing as a beam extracting system of electrodes,and plane 116 serving as a high voltage plane associated with filament120. Shield 117 is also associated with plane 116 and filament 120,being connected thereto via lead 118. Electrons emitted by filament 120are accelerated by electrodes 110-115 and become a high velocityelectron beam 123 which is capable of performing various typesof desiredwork. In some applications the electron beam is scanned in a rectilinearfashion after acceleration to provide electron irradiation of a width ofmaterial. Power for the various elements of accelerator 200 istransmitted thereto from power supply 100 by way of a graded cable 300.Graded cable 300 consists of a plurality of concentric conductors210-270 surrounding a central wire 280. The seven concentric conductors210-270 are connected at one end to planes 21-27 in power supply 100 vialeads 61-67 and at the other end to planes 1 -116 in accelerator 200 vialeads 130-135 and lead 118 together with shield 117. In this fashion thegraded voltages on equipotential planes 21-27 in power supply 100 aredirectly connected to associated planes 110-116 in accelerator 200 via asingle cable. Central wire 280 carries AC power from isolationtransformer 75 to filament 120 to heat filament 120 and produce emissionof electrons for acceleration.

FIGS. 2 and 3 show, respectively, a side and a top view of themechanical arrangement of power supply 100 and one end of graded cable300 associated therewith. It should be understood that the variouselectrical elements such as resistors, capacitors, and'rectifiers, shownschematically in FIG. 1 are physically located between the individualdiscs serving as equipotential planes. As shown, high voltagetransformer 70 occupies one whole side of the power supply enclosure,and isolation transformer 75 occupies a comer of the enclosure on theother side thereof.

Discs 1-27 which serve as equipotential planes are mounted in twoseparate stacks between top 28 and bottom of the enclosure. Disc 3 isshown in cross section to illustrate the typical cross-sectional profileof discs 1-27. As can be seen, the discs which serve as equipotentialplanes carrying the highest DC voltage (300 kv.) are separated from thetop 28 and bottom 20 of the enclosure, and therefore do not look withtheir flat sides at a ground plane. The dual stack arrangement serves toconserve space in the power supply, and thus the power supply enclosurecan be smaller. This is a distinct advantage from a cost savingsstandpoint since the enclosure will cost less and the factory orlaboratory space needed to house the power supply can be reduced.Moreover, the separation of the highest voltage planes from the top andbottom of the enclosure with intervening graded voltage planes reducesthe likelihood of sparking in the power supply, and this ishighlyadvantageous because such discharges cause an expensive failure of thesystem involving likely damage to rectifiers and other elements whichmust then be replaced during consequent down time.

One of the primary advantages of the graded plane power supply is thesize reduction achieved by grading the voltage gap between 300 kv. andground with a plurality of equipotential planes. As is well known, thepower supply enclosure will be filled with an insulating fluid,typically a nonconductive oil. The separation distance required betweena 300 kv. point and a ground point with only insulating oil interveningwould be very great, but considerably less overall separation isrequired when graded planes intervene. This follows from the nonlinearrelationship between insulator thickness and breakdown voltage so thatless intervening distance with insulating fluid filling it is requiredwhen graded planes are used between 300 kv. planes and ground planes. Afurther advantage is the added stability of the power supply achieved asa result of the graded equipotential planes serving to provide a uniformvoltage gradient throughout the power supply enclosure.

As shown in FIG. 2, capacitor equipotential planes 16-19 are mounted onthree insulating columns or poles 43; and the remainder of the capacitorequipotential planes 11-15 are mounted on another three insulatingcolumns 42. Resistor equipotential planes 21-27. are shown mounted on asingle insulating column 29 which is supported on plane 16. Plane 27 isassociated with the top 28 of the power supply enclosure. Rectifierequipotential planes 1-10 are shown mounted on a single insulatingcolumn 33 which is supported on plane 11. Plane 1 is associated with thetop 28 of the power supply enclosure. Typically, planes 1-10 with column33 and planes 21-27 with column 29 will be mechanically constructed sothat they can be removed from the enclosure as a unit for ease inservicing the power supply. Moreover, an additional plane or disc couldbe added at the bottom of rectifier series 1-10 with a jack-in relationto plane 11 to enable reversal of power supply polarity by flipping overthat unit.

Resistors 51, 52, and 53 are shown connecting plane 11 to plane 21.These resistors are limiting resistors which protect the rectifiersassociated with planes 1-10 from surge current in the event of a shortcircuit in the accelerator or the cabling.

As shown in FIGS. 2 and 3, graded cable 300 extends through planes21-27, and the respective concentric conductors 210-270 are bared atappropriate levels for connection to the respective planes. Center wire280 extends through plane 21 and connects via lead 76 to isolationtransformer 75. It should be readily understood that other mechanicalassociations between graded cable 300 and planes 21-27 and transformer75 could also be implemented.

A 300 kv. power supply of the arrangement shown in FIGS. 2 and 3 can beconstructed to have overall dimensions of approximately 5 6X5 feet,which is about half the size of many power supplies of otherconstruction having the same rating. An actually constructed embodimenthas been operated at 300 kv. with about 30- kilowatt-output power. Froman industrial equipment standpoint a power supply of this rating andthis overall size constitutes a real achievement. Furthermore, extensionof the basic concepts or features of its construction to achieve powersupplies with a 1,000 kv., kw. or higher rating is considered to beattainable with only relatively slight increases in overall size,possibly with greater numbers of graded planes in each stack.

In FIG. 4, a 300 kv. electron accelerator 400 of a particular prior arttype is shown. A pair of bulky cables 501 and 502 bring the high voltageDC power supply and an AC signal impressed on the high DC voltage. Inthis case the AC signal is transformed down'to a lower voltage bytransformer 350 before applying it to the filament, although this is notalways necessary since a lower voltage, higher current signal could beproduced in the power supply and carried by the cables directly to thefilament.

A large number of accelerating electrodes, for example the 20 electrodes310-330 shown in FIG. 4, are required in the accelerating column forstable operation of this type of accelerator; and a resistor network 335is required to provide a voltage dividing network for the respectiveelectrodes. Individual rings of insulating material 331 support theelectrodes, and the rings and electrodes are sealed so as to form avacuum tight enclosure. The individual resistors in network 335 arerequired to be small and yet to be capable of operating at high power,and these two requirements are not readily reconciled. A rather highmagnitude of current through the resistors of this network is desirableso that a stray electron beam will not disrupt the value of their IRdrop, but a practical limit is placed on the possible current valuebecause of the heat that is generated. Auxiliary cooling could beprovided, but this is undesirable. Therefore, a 0.5 ma. current is atypical limit on the current through this resistor network. Expandingthis design concept to provide an accelerator with a still highervoltage, higher power rating is not considered feasible except bygreatly increasing the length of the accelerating column.

Larger power transmission cables would also be required for highervoltage operation. Consequently, it is believed that inherentlimitations are present in this type of prior art accelerator design andthat these limitations make this design a relatively unattractiveapproach to the construction of high voltage accelerators.

Contrasted to the prior art design shown in FIG. 4, an accelerator 200of a graded plane design is shown in FIG. 5 in approximate relative sizerelationship. The comparative simplicity of design and reduction in sizeare apparent from this side-by-side comparison. Graded accelerator 200has seven graded planes 110-116 connected to seven graded conductors2l0270 in graded cable 300 via leads 130-135 and 118. These seven gradedplanes are mounted on a triangular array of three insulating columns 138(only one shown) and cable 300 passes directly through the respectiveplanes as in power supply 200 in FIG. 2. Each of the graded planes 111-115 may have the same cross-sectional profile as that of plane or disc 3in the power supply shown in FIG. 2.

Various types of construction can be employed for accelerating column136, which is basically composed of internal electrodes (not shown) andcylindrical insulating members 137 mounted in a sandwichlike arrangementwhich must form a vacuumtight seal. The electrodes may be integral partsof their respective planes or discs, or they may be separate elementsmounted to their respective planes. Conceivable, planes 111-416 may bemade much smaller in diameter than shown in FIG. 5 so that the lip ofthe planes extending out from column 136 is only wide enough toaccommodate the passage therethrough of the respective segments of cable300. In such a construction, insulating columns like column 138 may notbe required for supporting planes 111-416, rather the insulator rings137 could themselves support the planes.

Typically a cylindrical, gastight shield will be mounted to base plane110 and be filled with a nonconducting fluid, typically an insulatinggas. This insulating gas provides the electrical insulation betweenrespective planes, and prevents discharges or sparking therebetween.Conceivably planes 110- 116 could be surrounded by a vacuumtightenclosure with a high internal vacuum. This would further reduce thechances of sparking between planes, and it might make it possible toeliminate central accelerating column 136 altogether.

A readily apparent size advantage is achieved by constructing anaccelerator according to the graded plane design as illustrated in FIG.5. Principally, the size difference results from the shorter insulatingcolumn with fewer electrodes. This is made possible by locating thevoltage divider resistors in the power supply where they can be cooledefficiently and thus can support a heavier current (on the order of 2.0ma.) to stabilize the IR drop between respective planes in theaccelerator. Also, the graded planes themselves provide for more uniformdistributions of voltage gradients in the accelerator column area, andthis provides for more stable operation of the accelerator with lesslikelihood of discharges between planes or between acceleratingelectrodes. Thus, the distance between planes 110 and 116 in accelerator200 in FIG. 5 may be as little as 10 inches compared to a distance ofaround 18 inches between planes 330 and 340 in accelerator 400 in FIG.4. Moreover, as for power supply 100, it is believed that extension ofthis design concept to accelerators of greater than 300 kv. potential isreadily achievable.

Additional important advantages attend the requirement of only one cable300 to connect accelerator 200 to an appropriate power supply. Theseadvantages include the ease of installation where the interconnectingcable is to be carried in conduit and the size advantage of the gradedcable itself which is smaller in diameter than either of the cables 501and 502 in FIG. 4.

In FIG. 6 a particular construction of a graded cable is shown. A hollowcopper tube 270 carries internally a wire 280 having a thin layer ofinsulation 416 thereon. A layer of insulation 415 surrounds copper tube270, followed by a layer of conducting material 260 which is shown as athin layer of metallic foil but may also be a layer of braided copper orany other conducting material. Braided copper has proved to beadvantageously employed since it has greater resilience than a metalfoil and is thus less likely to break under bending stress applied tothe cable. Similar layers of insulating material 403 to 414 interspersedwith layers of conducting material 220 to 250 round out the 8 conductorcable. 210 designates a rather thick layer of braided copper which formsthe ground return braid of the cable which is, in turn, covered by afinal layer of insulating material 401.

A process which has been employed for making relatively short (50 feet)lengths of this type of cable involves starting with copper tube 270 anddisposing a length of a thin-wall, heat-shrinkable plastic tubing overit. Then the tubing is heated so that it shrinks over the copper tubeand is bound thereto, forming insulating layer 415. A single layer ofaluminum foil (e.g., approximately 4 mills thick) or, alternatively, alayer of braided copper (e.g., approximately 10 mills thick) is disposedover layer 415 to form conductor 260. Then another length ofheat-shrinkable plastic tubing is disposed over conductor 260 and heatedto bind both to the previously built-up structure. Second and thirdlengths of tubing may be employed to increase the thickness of theinsulating layer as required. Repeating the above procedure enables oneto build up any desired number of concentric conductors.

Using this procedure, starting with a 0.298 inch OD copper tube andusing thin aluminum foil for conducting layers, a cable as shown in FIG.6 has been constructed. The resulting overall diameter of the cable wasabout 1.2 inches, and the cable was successfully tested with 300 kv. oncopper tube 270 and with approximately 60 kv. voltage drops betweenrespective conductors 270, 260, 250, 240, 230, 220, and 210. A cable hasalso been constructed with braided copper as the conducting layers, andit has only slightly larger diameter because of the thicker layers ofconducting material. It is believed that greater than 300 kv. voltagescan be carried by these cables, and there appears to be no reason tosuspect that similarly constructed cables cannot be fabricated to carryupwards of 1,000 kv. perhaps with ten kv. gradings between innermost andoutermost conductors. It should be clearly understood that otherembodiments of graded cable and other methods for making it are withinthe scope and purview of this invention.

It should be understood that this invention is not limited to use inconnection with accelerators or even graded cable transmission systemsand, furthermore, is not limited to voltage doubler-type power suppliesor to power supplies producing negative voltages. Thus, it is apparentthat numerous modifications could be made by those skilled in the artwithout departing from the scope of this invention as claimed in thefollowing claims.

I claim:

1. In a high voltage direct current power supply wherein the high DCvoltage is produced by employing a plurality of electrically operativeelements such as rectifiers, capacitors, and the like, the improvedarrangement comprising:

power supply enclosure means for containing a quantity of electricallyinsulating fluid;

a plurality of voltage grading means mounted within said enclosure meansfor stabilizing the high voltage produced, each of said voltage gradingmeans including a plurality of equipotential planes mounted inspaced-apart relation to each other with a stepwise gradient of voltagesfrom said high voltage on a central plane to a ground reference voltageon an end plane, said electrically operative elements being mountedbetween individual ones of said equipotential planes and being connectedtherebetween to produce said stepwise gradient of voltages.

2. The arrangement as claimed in claim ll, wherein said enclosuremeansincludes a pair of opposing walls having substantiallygroundreference potential thereon; the number of said voltage gradingmeans is three; the first, second, and third ones of said voltagegrading means having primarily associated therewith rectifiers,capacitors, and resistors, respectively; said first, second and thirdvoltage grading means being arranged in two separated stacks betweensaid opposing walls such that the equipotential planes which carry thehighest DC voltage are spaced from said opposing walls with at least oneequipotential plane which carries a lower voltage is interposed betweeneach of said last-mentioned planes and said opposing walls, therebyreducing the tendency for sparking to occur in said power supply.

3. In a high voltage, direct current power supply of the voltagedoubler-type having the components thereof immersed in a bath ofelectrically insulating oil, the improved arrangement comprising:

a plurality of equipotential planes operatively grouped as rectifierplanes, capacitor planes, and resistor planes; said planes beingarranged in two separated stacks of spacedapart planes with all of saidrectifier planes and a first portion of said capacitor planes in a firstone of said stacks and with all of said resistor planes and theremaining portion of said capacitor planes in a second one of saidstacks; said planes in each of said stacks being graded voltagewise withlower voltages on planes at each end and higher voltage on centralplanes.

4. The arrangement as claimed in claim 3, wherein said two stacks ofplanes are mounted between a pair of opposing walls providing groundreference potential thereon; one of said walls providing groundpotential for said rectifier planes and said resistor planes; the otherof said walls providing ground reference potential for said capacitorplanes and being electrically insulated from said first portion of saidcapacitor planes.

5. In a high voltage, direct current power supply:

a tank having electrically conducting walls and being capable ofcontaining a column of electrically insulating fluid;

a high voltage transformer mounted on the bottom of said tank;

a plurality of electrically conducting discs mounted in spaced-apartrelation in two separate stacks between two opposing walls of said tank;

a plurality of rectifiers coupled in series between a first preselected,centrally located disc in one of said stacks and one of said opposingwalls with successive intervening discs serving as graded equipotentialrectifier planes;

' a plurality of capacitors coupled in series between said firstpreselected disc and the disc adjacent the other of said walls withsuccessive intervening discs serving as graded equipotential capacitorplanes;

a plurality of resistors coupled in series between a second preselected,centrally located disc in the other of said stacks and one of saidopposing walls with successive intervening discs serving as gradedequipotential resistor planes;

a plurality of capacitors coupled in series between the other of saidopposing walls and the disc adjacent said second preselected disc withsuccessive intervening discs serving as graded equipotential capacitorplanes;

means for direct current connecting the series of capacitor coupleddiscs in one stack with the series of capacitor coupled discs in theother stack;

at least one series resistor connected between said first and secondpreselected discs; and

circuit connections between said high voltage transformer and apreselected one of said rectifier planes and a preselected one of saidcapacitor planes; whereby said power supply is capable of producing ahighly stable high DC voltage on said first and second preselecteddiscs.

6. Apparatus as claimed in claim 5, wherein said plurality of rectifiersand said rectifier planes are so constructed and arranged that the maybe removed from said tank as a single structural unit or ease ofmaintenance and for ease in changing the polarity of the high DC voltageproduced by said power supply; and said tank includes an access portassociated with said structural unit.

7. Apparatus as claimed in claim 6, wherein said plurality of resistorsand said resistor planes are so constructed and arranged that they maybe removed from said tank as a single structural unit for ease ofmaintenance thereof; and said tank includes a second access portassociated with said structural unit.

1. In a high voltage direct current power supply wherein the high DCvoltage is produced by employing a plurality of electrically operativeelements such as rectifiers, capacitors, and the like, the improvedarrangement comprising: power supply enclosure means for containing aquantity of electrically insulating fluid; a plurality of voltagegrading means mounted within said enclosure means for stabilizing thehigh voltage produced, each of said voltage grading means including aplurality of equipotential planes mounted in spaced-apart relation toeach other with a stepwise gradient of voltages from said high voltageon a central plane to a ground reference voltage on an end plane, saidelectrically operative elements being mounted between individual ones ofsaid equipotential planes and being connected therebetween to producesaid stepwise gradient of voltages.
 2. The arrangement as claimed inclaim 1, wherein said enclosure means includes a pair of opposing wallshaving substantially ground reference potential thereon; the number ofsaid voltage grading means is three; the first, second, and third onesof said voltage grading means having primarily associated therewithrectifiers, capacitors, and resistors, respectively; said first, secondand third voltage grading means being arranged in two separated stacksbetween said opposing walls such that the equipotential planes whichcarry the highest DC voltage are spaced from said opposing walls with atleast one equipotential plane which carries a lower voltage isinterposed between each of said last-mentioned planes and said opposingwalls, thereby reducing the tendency for sparking to occur in said powersupply.
 3. In a high voltage, direct current power supply of the voltagedoubler-type having the components thereof immersed in a bath ofelectrically insulating oil, the improved arrangement comprising: aplurality of equipotential planes operatively grouped as rectifierplanes, capacitor planes, and resistor planes; said planes beingarranged in two separated stacks of spaced-apart planes with all of saidrectifier planes and a first portion of said capacitor planes in a firstone of saiD stacks and with all of said resistor planes and theremaining portion of said capacitor planes in a second one of saidstacks; said planes in each of said stacks being graded voltagewise withlower voltages on planes at each end and higher voltage on centralplanes.
 4. The arrangement as claimed in claim 3, wherein said twostacks of planes are mounted between a pair of opposing walls providingground reference potential thereon; one of said walls providing groundpotential for said rectifier planes and said resistor planes; the otherof said walls providing ground reference potential for said capacitorplanes and being electrically insulated from said first portion of saidcapacitor planes.
 5. In a high voltage, direct current power supply: atank having electrically conducting walls and being capable ofcontaining a column of electrically insulating fluid; a high voltagetransformer mounted on the bottom of said tank; a plurality ofelectrically conducting discs mounted in spaced-apart relation in twoseparate stacks between two opposing walls of said tank; a plurality ofrectifiers coupled in series between a first preselected, centrallylocated disc in one of said stacks and one of said opposing walls withsuccessive intervening discs serving as graded equipotential rectifierplanes; a plurality of capacitors coupled in series between said firstpreselected disc and the disc adjacent the other of said walls withsuccessive intervening discs serving as graded equipotential capacitorplanes; a plurality of resistors coupled in series between a secondpreselected, centrally located disc in the other of said stacks and oneof said opposing walls with successive intervening discs serving asgraded equipotential resistor planes; a plurality of capacitors coupledin series between the other of said opposing walls and the disc adjacentsaid second preselected disc with successive intervening discs servingas graded equipotential capacitor planes; means for direct currentconnecting the series of capacitor coupled discs in one stack with theseries of capacitor coupled discs in the other stack; at least oneseries resistor connected between said first and second preselecteddiscs; and circuit connections between said high voltage transformer anda preselected one of said rectifier planes and a preselected one of saidcapacitor planes; whereby said power supply is capable of producing ahighly stable high DC voltage on said first and second preselecteddiscs.
 6. Apparatus as claimed in claim 5, wherein said plurality ofrectifiers and said rectifier planes are so constructed and arrangedthat they may be removed from said tank as a single structural unit forease of maintenance and for ease in changing the polarity of the high DCvoltage produced by said power supply; and said tank includes an accessport associated with said structural unit.
 7. Apparatus as claimed inclaim 6, wherein said plurality of resistors and said resistor planesare so constructed and arranged that they may be removed from said tankas a single structural unit for ease of maintenance thereof; and saidtank includes a second access port associated with said structural unit.